Apart from Gayenne, who has done VOs for the weekend presenters, ie Kylie Pentelow? As it doesn't sound like that Gayenne has done them?
Believe it or not, they have all been recorded by Gayenne Potter since January 2013. I think her recent lack of consistency in delivery is due to the way she records them. Gayenne has a home recording studio and for the initial batch this was sent via ISDN to ITN where it was recorded as a WAV file. She got immediate direction from staff at ITN as to what she was doing.
At some point after that, Gayenne seems to have introduced the ability to record them herself and send the recordings to ITN electronically. The problem with this method is that she doesn't have the benefit of a Director and Sound Mixer. She records a few takes of each VO and then sends them to ITN. In the good old days, Andrew Burt's VOs would be recorded on DAT at ITN and he could receive immediate feedback from the Director and further takes could be recorded. There are some amusing examples where he mispronounced (Denis) Tuohy as "chewy" and (Shiulie) Ghosh as "gosh" but could be corrected straight away. I think the problem now is that there isn't as much quality control over the process as there used to be. However, it's probably outweighed by the positives of it being a cheap and flexible way of recording the VOs. They can pretty much get Gayenne to record VOs for presenters on location on the day. That was impossible in times gone by and led to all sorts of weird and wonderful edits being made, usually on 1/4" tape or on the 360 Systems Short/cut Editor.
One amusing anecdote about James Faulkner's initial recording session in 2009: he said Charlene (White) with a hard "ch" sound rather than "sh". Somehow this slipped by the technical crew and was only picked up once work had begun on chopping up the recording session into individual clips for TX. James had visited ITN in person (much like Andrew Burt) so it was too late to get him back to record it again and, if memory serves, Charlene was the Morning News presenter on the day of the rebrand. So, one of the Sound Mixers cut the "sh" off (Chris) Ship and edited it onto Charlene's VO. Nobody was any the wiser and that version was actually never replaced! With the VO always being mixed with music, the edit wasn't noticeable.